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SubjectRe: [PATCH 5/7] FUSE: implement ioctl support
Miklos Szeredi wrote:
> On Thu, 28 Aug 2008, H. Peter Anvin wrote:
>> This is *hard* to get right, and we screw this up in the kernel with
>> painful regularity. The throught of having user-space processes, which
>> don't have access to the kernel locking primitives and functions like
>> copy_from_user() dealing with this stuff scares me crazy.
> What issues exactly are you thinking of?

Memory changing underneath you. It can be dealt with by very careful
sequencing only.

>> That is why I'm suggesting using an in-kernel linearizer.
> Lots of complexity, ugh... Even Tejun's current scheme is better IMO.

And then you get *no* privilege separation, for one thing, so why even
bother doing it in userspace?


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